Choosing Your Cylinder Heads - Casting Call

How much cylinder head do you need? Just enough, as we show in this dyno test.

Choosing cylinder heads for your small-block is easy, right? All you have to do is look for the one that offers the most flow. Well, truth be told, it really isn't as easy as all that, and that's a good way to end up with a doggy engine. The airflow offered by the cylinder head is certainly an indicator of power potential, but airflow alone is far from a guarantee.

Just because the head flows enough to support 500, 600, or even 700 hp, doesn't mean your engine will utilize every last cfm offered by the head casting. In reality, very few street or strip engines tax the flow limits of their respective cylinder heads. For most applications, the combination is limiting the potential of the cylinder heads and not the other way around.

The good news is this means choosing the right cylinder head for your application might not mean choosing the most expensive one with the highest flow rate. To put this theory to the test, we grabbed a pair of quality cylinder heads from Dart and compared its CNC-ported 227 head to a smaller as-cast 180 on a healthy small-block. The results might surprise you.

While this may not seem like a fair fight, the reality is that the airflow and even power numbers are not the only consideration in this comparison. The cost factor must also be applied, as (given the chance), we would all choose CNC-ported heads. Unfortunately, most enthusiasts are on a budget and would give up a few horsepower if it saved a few bucks. What every enthusiast is looking for is to maximize the bang for his or her buck, and why buy more cylinder head than your engine can use? The question now is how much is too much?

The answer came from Dart in the form of two small-block cylinder heads. The Pro 1 180cc as-cast head offered exceptional flow at a very cost-effective price ($736.04 per head at Summit Racing). It could not compete with the flow rates offered by the Pro 1 CNC 227 heads, but is the extra airflow and power worth the substantial cost difference between these two heads on this application? At Summit, some of the CNC'd 227 heads were $1,275 apiece. If this was a race application and we had to make every last ounce of power to win, the cost would be justified, but how about a typical street/strip application?

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Since we were testing two sets of Dart Pro 1 heads, what better test mule than one of Dart's SHP short-blocks? Displacing 372 ci, the stroker small-block featured a Dart block, Scat crank and rods and forged JE pistons.

The short-block was augmented with a Crane hydraulic roller cam, an Edelbrock Super Victor intake and Holley Ultra HP carburetor. The trick Crane hydraulic roller lifters and matching valve springs allowed this small-block to buzz right up to 7,000 rpm without fear of valve float.

Crane also supplied a set of 1.5 ratio Gold rockers and a double roller timing chain, while MSD stepped up with a crank-trigger ignition system. Completing our test mule was a set of 1 3/4-inch headers mufflers, and an Aeromotive A1000 fuel system to supply the necessary go-go juice.

Check out the photos and captions for a full rundown on how the as-cast Dart heads compared to the CNC-ported version.

10 Each set of Dart heads was run with 1.75-inch long-tube Hooker headers feeding race mufflers.

11 After timing sweeps and carb jetting, the 372-inch mill with 180cc heads produced 510 hp at 6,200 rpm and 479 lb-ft at 5,000 rpm.

12 Next up were the Dart Pro 1 CNC-ported 227 heads. Full CNC porting brought the intake port volume up to 227cc and the flow rate up to 309 cfm.

13 The flow rate of the 85cc exhaust ports was equally impressive, checking in at 226 cfm.

14 Everything was bigger on the 227 heads, including the fully CNC-ported, 66cc combustion chamber and 2.08-inch intake valve. The exhaust valve remained at 1.60 inches.

15 Off came the as-cast 180cc heads and on went the CNC-ported Dart Pro 1 227s.

16 Equipped with the larger 227 heads, the peak numbers jumped to 520 hp and 476 lb-ft of torque. Though the CNC heads will easily support 625 hp (or more), this milder stroker application worked almost as well with the smaller as-cast 180 heads. For most street enthusiasts, the as-cast Pro 1s seem to be the hot set up.

17 The surprise is not that the CNC-d Dart Pro 1 227 heads produced more horsepower than smaller as-cast 180 heads, but how well the as-cast head did. In terms of peak power, the CNC heads offered only an additional 10 hp and actually lost out by 3 lb-ft to the smaller heads in peak torque (476 vs. 479 lb-ft). This test was not about which head makes more absolute power; it was about which head was best suited to this application. Though a 500-plus hp stroker small-block certainly qualifies as a healthy street motor, the mere fact that the as-cast, Pro 1 head did so well demonstrated they were serious players. This test also demonstrated that the larger and more powerful CNC-ported 227 head would be better suited to a combination with wilder cam timing, increased displacement and/or higher compression. The airflow offered by the CNC heads indicates they will support well over 625 hp on the right application, so make sure to choose wisely when selecting head gear for your engine.